Abstract
Various quinones with vitamin K activity have been assayed in order to establish the comparative potencies of these compounds in relation to a common reference standard. The reference standard is an hexane extract of dried alfalfa equivalent in potency to 1 g of dried alfalfa per cc. This reference standard at 2 or more levels has been employed in all of our assays for the past 2 years. A secondary reference standard consisting of a sample of dried alfalfa has also been preserved. Neither of these standards has shown any loss of total or relative activity. In periodic assays the potency of the second reference standard has been obtained as 1.09, 1.03, 1.07, and 1.06 cc of the first standard per gram.
Some assays have been conducted as we have already described, 1 that is, by placing the supplement in the diet of depleted chicks and determining the prothrombin clotting time after 7 or more days. More recently, 2 after a depletion period of 10 to 14 days, we have given the supplement orally for 4 days and have determined prothrombin clotting time on the fifth day. Certain supplements have been assayed by both procedures and have given identical results. In a few cases, where evidence of loss of the supplement in the diet was encountered, the oral feeding was relied upon entirely. In all asays, the reference standard was employed at 2 or more levels in order to establish values for interpolation and calculation of potencies in terms of the standard. This may be done by means of the linear relation between the reciprocal of the prothrombin clotting time and the logarithm of the vitamin K dosage. 1 No “master curves,” “response curves” or arbitrarily fixed values are required in our method.
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